Antibiotic pollution is one of the key routes by which bacteria are able develop resistance to the life-saving medicines, rendering them ineffective for human use. “A lot of the resistance genes we see in human pathogens originated from environmental bacteria,” said Prof William Gaze, a microbial ecologist at the University of Exeter who studies antimicrobial resistance but was not involved in the study.

The rise in antibiotic-resistant bacteria is a global health emergency that could kill 10 million people by 2050, the UN said last month.

The drugs find their way into rivers and soil via human and animal waste and leaks from wastewater treatment plants and drug manufacturing facilities. “It’s quite scary and depressing. We could have large parts of the environment that have got antibiotics at levels high enough to affect resistance,” said Alistair Boxall, an environmental scientist at the University of York, who co-led the study.